Fiberboard construction



Patented Jan. 1, 1952 FIBERBOARD CONSTRUCTION Glen E. Babcock, Vernon L.Johnsen, and Allan K. Smith, Peoria, 111., assignors to the UnitedStates of America as represented by the Secretary of Agriculture NoDrawing. Application February 23, 1951, Serial No. 212,477

4 Claims. (Cl. 15414 1) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) This application is made underthe act of March 3. 1883, as amended by the act of April 30, 1928, andthe. invention herein described, if patented in any country, may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes throughout the world without thepayment to us of any royalty thereon. v

This application is a continuation-impart application of Serial No.94,533, filed May 20, 1949, now abandoned.

This invention relates to the manufacture of laminated fiberboard usefulin the manufacture of industrial containers, such as cartons, boxes,barrels and the like.

This invention has among its objects the provision of a special glue forfiberboard construction which is novel and economical, and whichutilizes as its major ingredients a significant proportion ofagricultural material. Another object of the invention is the provisionof a process whereby laminated fiberboard may be fabricated simply andat a greatly reduced cost.

Fiberboard laminating glues heretofore used in industry comprise for themost part starches or degraded starches fortified with synthetic resins,such as the urea type or vinyl type. Urea resins result in a short potlife and a brittle film, although they have fair water resistance. Vinylresins give satisfactory general results but the cost is excessive.

We have discovered a glue formulation and a process of employing itwhich results in a highquality laminated fiberboard product withsurprisingly good water resistance and excellent strengthcharacteristics. The glue possesses characteristic which render itparticularly useful in the paper laminating field. This formulationconsists of:

About from 10 to 18 parts of soy fiour,

About from 10 to 2 parts of soy protein,

About from 2% to 10 parts of a 20 percent solution of one of the groupconsisting of an ammonium resin and the corresponding alkali metal saltsthereof,

About from 2 to 10 parts saponified rosin,

About from 10 to 15 parts of an 8 percent sodium hydroxide solution. andsufficient water to make a spreadable glue containing about from 18 to26 percent solids.

The soy flour, which includes soy meal, is that available as an articleof commerce, having an oil content of about 1 percent or less. The soyprotein employed is isolated soybean protein contaimng percent or moreprotein. The sum of the parts of soy flour and soy protein in thisformula, should equal approximately 20 parts. For example, when theproportion of one is increased within the range specified, theproportion of the other is correspondingly decreased. Since the soyflour is the cheaper adhesive ingredient, it is usually desirable toemploy it in maximum proportion.

The ammonium resin is readily available as an article of commerce. It isa complex ammonium salt of a copolymer of a four carbon, alpha, betaunsaturated dicarboxylic acid with styrene, such as that obtained by theemulsion copolymerization of a soluble salt of fumaric acid and styrene.It has a molecular weight of about from 2000 to 7000 and contains asubstantial proportion of acidic groups. It is water-soluble and thealkali metal salts thereof, such as the sodium salt, are alsowater-soluble. It functions as a tackifier, enabling the glue compoundto hold the paper board together until the protein components set thebond in the final waterproof form. It results in a temporary bondsuflicient to tear the paper, when the laminate is forcibly separated,in a few seconds after pressure has been applied by means of pressurerolls. Thus the glue may be used with production machinery involvingspeeds up to 400 lineal feet per minute and higher.

The saponified rosin functions to stabilize the viscosity of the glueand supplements the tackify ing action of the ammonium resin. This rosiningredient could be omitted if the proportion of the ammonium resin wereslightly increased, nevertheless we prefer to employ it in the statedproportions, since this results in a more economical glue formulation,the ammonium resinbeing relatively more expensive than the saponifiedrosin.

The amount of sodium hydroxide used corresponds to that necessary toadjust the pH within the range of 10.5 to 11.0 of the formulated glue.

The above specialty glue has been found to give entirely satisfactoryresults in the paper laminating field and compares favorably with theexpensive starch-vinyl resin specialty glues of the prior art.Nevertheless, we have discovered that this glue has certain limitationswhen employed as such in the usual commercial fabrication steps in themanufacture of laminated fiberboard. It gives excellent results up to 2or 3 hours after the glue composition has been made up. After this time,the viscosity of the glue increases rapidly until it soon reaches avalue 3 to times the normal operating viscosity, and finally becomes toothick to spread. The tackiness of the glue is also reduced to anunsatisfactory value; an excessive amount of scrap is produced becausethe glued paper fails to hold together during fabrication processes.

For many purposes the above glue is distinctly advantageous, and forfabrication processes requiring short times it is possible to producewith the glue, laminated products of excellent quality.

We have further discovered that the pot life of the above glue can beincreased up to 96 hours and longer, and the original tackinesspreserved by the simple expedient of adding suflicient sodium hydroxideto the glue to maintain the pH within the range of 10.5 to 11.0. We havelearned that the original glue as formulated above begins to evolveammonia after an hour or so, the pH dropping to about 10.4 or less. .Webelieve it is this change in pH which causes the glue to become thickand to lose its tackiness. In any event, the addition of sodiumhydroxide in amounts suflicient to maintain the pH within the desiredrange results in indefinitely prolonged pot life and maintenance of thenecessary tackiness in the glue.

The addition of sodium hydroxide is accomplished conveniently during theactual fabricating process by simply adding the required amount ofsodium hydroxide as soon as the pH falls below the desired range.

We have further discovered that the above process may be modifiedadvantageously and the periodic addition of sodium hydroxide avoidedentirely by simply converting the ammonium resin to the correspondingsodium resin. The converted resin is employed in the originalformulation. By doing so, the difficulties of shortened pot life anddecreasing tackiness are entirely eliminated. The conversion of theresin may be accomplished in known manner, such as for example, bytreating the stock solution with sodium hydroxide and removing theevolved ammonia by agitating, aerating, and/or heating the resinsolution.

The following specific examples illustrate the invention. The partsgiven are by weight.

The above glue had a solids content of 20 percent and if kept in closedcontainers was stable for long periods of time. At room temperature theglue is transformed into a soft gel. At 60 C. and above, it is easilyspreadable, the soft gel disappearing upon heating. In accordance withpresent paper laminating practice, glue formulae are employed at about60 0, depending on the type of board being glued. High absorbent stockis run at lower temperatures to conserve glue. The glues employed mustbe quite thin at these temperatures, becoming much thicker on cooling toroom temperature. The increased viscosity on rapid cooling is adesirable, if not necessary factor in developing a strong tack. Theglue, formulated as specified above, was used in a commercial scalefabrication for producing 4- ply laminated container board. It gaveexcellent results for the first two hours of operation, but after thistime the viscosity of the glue began to increase, and the tackinessdecreased until the amount of scrap produced began to be excessive.

Example 2 A 1000 gallon batch of glue was formulated as specified inExample 1 and was employed, as in Example 1, in the manufacture ofmulti-ply laminated container board. In this example, the pH of the gluewas maintained at approximately 10.7 to 10.8 by the periodic addition ofsodium hydroxide. The products were of excellent quality, throughout thetrial run, which lasted for a half day. Half of the glue was heldovernight, and the batch used up on the following day. The results wereuniformly excellent. The viscosity of the glue remained at its originalvalue of approximately 30 poises when measured at 60 C. and thetackiness characteristic of the original glue remained substantiallyunchanged.

Example 3 A glue was formulated as specified in Example 1 with theexception that the sodium salt of the ammonium resin was substituted.This sodium salt was readily prepared as follows. Sodium hydroxide andthe ammonium resin were mixed at room temperature in the ratio of 1 partsodium hydroxide solids to 6 parts ammonium resin solids. The resultingsolution was allowed to dry. and as it dried, it evolved gaseousammonia. Alternatively, the aqueous solution, instead of being dried maybe heated and aerated to remove the F evolved ammonia.

This glue was employed to fabricate laminated fiberboard on a laboratoryscale. It had viscosity and tackiness characteristics substantiallyidentical with the glues of Examples 1 and 2, and was stable forindefinite periods of time involving several days. The laminatedproducts were pliable, and had excellent water resistance and strengthcharacteristics.

We claim:

1. A fiberboard laminating glue consisting of about from 10 to 18 partsof soy flour, about from 10 to 2 parts of soy protein, the sum of theparts of said soy fiour and soy protein equaling approximately 20 parts,about from 2 /2 to 10 parts of a 20 percent solution of one of the groupconsisting of the ammonium salt of a copolymer of a four carbon, alpha,beta unsaturated dicarboxylic acid with styrene and the correspondingalkali metal salt thereof, about from 2 to 10 parts saponified rosin,about from 10 to 15 parts of an 8 percent sodium hydroxide solution, andsufiicient water to make a spreadable glue containing about from 18 to26 percent solids, the amount of the said sodium hydroxide beingsuflicient to give a pH within the range of 10.5 to 11.0 to the glue.

2. The composition of claim 1, wherein the alkali metal salt is thesodium salt.

3. In a process for the manufacture of laminated fiberboard comprisingcoating individual sheets of fiberboard with glue and subjecting the 6laminated board to conditions of heat and pres- REFERENCES CITED thelmprovemfmt R employing a The following references are of record in theglue of the composition of claim 1 and main-tainme of this patent: ingthe pH of the glue within the range of 10.5 to

11.0 by periodic addition of sodium hydroxide. 5 UNITED STATES PATENTS4. A laminated fiberboard comprising a p u- Number Name Date rality offiberboard sheets bonded together by the 1,377,202 satow Sept, 13, 1932glue 01' claim 1. 2,315,402 DAlelio Mar. 30, 1943 GLEN E. BABCOCK.2,369,427 Bennett Feb. 13, 1945 VERNON L. JOHNSEN. 10 2,385,240 WareSept. 18, 1945 ALLAN K. SMITH.

1. A FIBERBOARD LAMINATING GLUE CONSISTING OF ABOUT FROM 10 TO 18 PARTSBY SOY FLOUR, ABOUT FROM 10 TO 2 PARTS OF SOY PROTEIN, THE SUM OF THEPARTS OF SAID SOY FLOUR AND SOY PROTEIN EQUALING APPROXIMATELY 20 PARTS,ABOUT FROM 2 1/2 TO 10 PARTS OF A 20 PERCENT SOLUTION OF ONE OF THEGROUP CONSISITNG OF THE AMMONIUM SALT OF A COPOLYMER OF A FOUR CARBON,ALPHA, BETA UNSATURATED DICARBOXYLIC ACID WITH STYRENE AND THECORRESPONDING ALKALI METAL SALT THEREOF, ABOUT FROM 2 1/2 TO 10 PARTSSAPONIFIED ROSIN, ABOUT FROM 10 TO 15 PARTS OF AN 8 PERCENT SODIUMHYDROXIDE SOLUTION, AND SUFFICIENT WATER TO MAKE A SPREADABLE GLUECONTAINING ABOUT FROM 18 TO 26 PERCENT SOLIDS, THE AMOUNT OF THE SAIDSODIUM HYDROXIDE BEING SUFFICIENT TO GIVE A PH WITHIN THE RANGE OF 10.5TO 11.0 TO THE GLUE.